Quoting keydiver:
It will display the AFR if you connect the 5 volt output of a wideband O2 setup perhaps, but that's about it.
According to Fullthrottle's site:
"Analog inputs: On the rear of the unit is a 3.5mm jack for connecting two 0-5 volt external signals. These signals can be displayed on the Scanmaster as well as logged to a PDA/PC. If a wideband Air/Fuel signal is connected, the Scanmaster 3 can be configured to display Air/Fuel ratio as the default display. The analog data can be displayed as boost (2 bar, 2.5 bar, 3 bar) and Air/Fuel ratio."
So, my statement above still applies. You can use one of the extra analog inputs on the back of the ScanMaster and have it display the AFR *IF* your O2 box has a 0-5 volt output to connect to it.